There are numerous circumstances in which blades are mounted on drums and in which it is desired to sharpen the blades after they have been dulled by protracted operation.
As one suitable example, mention can be made of a wood chipping machine in which branches and trunks of trees are reduced to chips by means of cutting blades on a rotating drum. Such chipping machines are relatively large and are powered, for example, by engines of 100 to 200 horsepower. Such machines are conventionally trailer mounted and a plurality of cutting blades, usually four, are mounted in slots in a steel drum approximately twelve inches in diameter and from nine to sixteen inches in width. The drum rotates at a high speed of from 2000 to 3000 R.P.M.
In order to maintain the efficiency of the chipping operation, the blades must be sharpened frequently. Conventionally, this is undertaken by removal of the blades from the drum and sharpening them while they are removed. Thereafter, the blades must be reset into the drum. The total operation requires at least two hours and it takes substantial skill to grind the cutting surface of the blade.
Attempts at hand grinding the blade have proved to be unsatisfactory in practice, since it is virtually impossible to maintain the necessary angle of the cutting surface on the blade.